Functional Java VS StreamEx

I made one (Before realizing it'd already been done) to backport newer language features to Java 8 and it was pretty easy to bundle it up as a maven plugin. But going back all the way to 4 will be a notable increase in difficulty. Retrolambda goes to 1.5 but not all the way to 4. You could hypothetically add a layer on top of it to support 1.5 -> 1.4. That or roll a fork of it.

I really like StreamEx. I do not know why people do not use it often, the syntax is just wonderful.

It gets more perverse if you need to flatMap, or transmute components of map types, etc. If you want even more power, take a look at https://github.com/amaembo/streamex. This sort of container manipulation bread and butter for business processing. I use it every day, sometimes with a dozen operations. This (with liberal use of `final` values) makes for some pretty functional-looking code.

I'll grant you the Kotlin or Scala version is slightly more compact. But not fundamentally different, like the Go version.

I (and the pretty much every language designer in the post-Java era) disagree with you about checked exceptions, but that's a whole different thread...